docs: def PartialDynamicSystem(self, ieq, variable):
          """
          returns dynamical system blocks associated to output variable
          """
          if ieq == 0:
              # U1=0
              if variable == self.variables[0]:
                  b1 = FunctionBlock(
                      self.physical_nodes[0].variable, self.max_torque, self.Tmax)
                  b2 = Saturation(self.commands[0], self.throttle, 0, 1)
                  b3 = Product(self.max_torque, self.throttle, variable)
                  return[b1, b2, b3]